This application claims the priority benefit under 35 U.S.C. xc2xa7119 to Singapore patent application no. 200004125-1, filed Jul. 24, 2000.
The present invention relates generally to the cooling of integrated circuits, and more particularly to a MEMS heat pump and cooling channels for cooling integrated circuits.
Today""s personal computers (PCs) and workstations are experiencing a rapid growth of accelerated clocking and computational speeds. PC clock speeds have progressed from the Intel Corporation 486(trademark) microprocessor speeds of 60 and 90 MHz, to the present Pentium III(trademark) clock speeds in excess of 600 MHz. Moore""s Law generally predicts a doubling of computing power and circuit complexity every year and a half or so.
The downside corollary to Moore""s Law, however, is that with doubling the number of devices in an integrated circuit (IC) consequently raises the amount of heat generated requiring dissipation. As an integrated circuit drives current between transistors it consumes power, producing waste heat that eventually transfers outward through the chip from the surface of the die. Generally, a PC chip designed for commercial use can withstand up to 150xc2x0 C. Exceeding that limit, however, will cause the chip to make errors in its calculations, or perhaps fail completely.
Current solutions in heat dissipation for chips include heat spreaders, heat sinks and fans. Heat spreaders, which generally are made of a tungsten-copper alloy and are placed directly over a chip, have the effect of increasing the chip""s surface area, allowing more heat to be vented upward. Similarly, heat sinks spread the heat upward through fins or folds, which are vertical ridges or columns that allow heat to be conducted in three dimensionsxe2x80x94length, width, and height, as opposed to the two-dimensional length and width of heat spreaders.
Fans within a computer housing can further aid heat dissipation from the chip or heat sink surface by convection. The amount of heat a fan dissipates away from a chip depends on the volume of air the fan moves, the ambient temperature, and the difference between the chip temperature and the ambient temperature.
The miniaturizing of integrated circuits have generally allowed for a reduction of operating voltages, resulting in lower heat production. However, chip shrinkage also means that heat-generating devices are packed closer together. Thus, the xe2x80x9cpower densityxe2x80x9d or the amount of heat concentrated at particular spots across the chip may begin to climb. As a consequence, heat is generated faster than it can be dissipated as higher clock speeds are demanded.
For example, PCs with a 486(trademark) microprocessor drew generally 12 to 15 watts, primarily concentrated in the processor. A power supply with an embedded fan was typically sufficient to circulate air and cool the inside of the PC chassis, while a passive heat sink could cool the processor. On the other hand, Pentium(trademark) processors from Intel Corporation consumed about 25 watts, thus requiring more cooling means than the passive heat sink for the processor alone. Similarly, the Pentium II(trademark) processor consumes about 40 watts, while future processors like the 64-bit Merced(trademark) may consume up to 65 watts. Other transistor-laden components must also contend with increasing heat generation: add-on cards; chipsets; graphics chips; and high-performance dynamic random access memory (DRAM).
There is, consequently, a need for improved heat dissipation from integrated circuits.
These and other needs are satisfied by several aspects of the present invention.
In accordance with one aspect of the invention a cooling system is provided for an integrated circuit. The system comprises a pump that circulates fluid within the integrated circuit. Desirably, the fluid carries heat from regions of heat generation to regions outside the integrated circuit.
In particular, Miniaturized Electro-Mechanical Structure (MEMS) technology is applied to create a miniature electromechanical pump within the chip. The illustrated pump comprises a piezoelectric actuator formed over a cavity in a structural layer. In other arrangements, a MEMS structure formed externally can be placed within the cavity, wired for operation, and sealed within the cavity. The cavity is in fluid communication with fluid-filled channels embedded within the integrated circuit.
The channels are formed, in the preferred embodiments, by etching trenches in a desired pattern, followed by lining the trenches by deposition. The deposition is engineered to create a continuous air gap along the trenches, and the cavity is opened to communicate with this air gap. Desirably, the air gap forms a closed loop including the cavity. After formation of the pump, these channels are then filled with fluid, such as argon, helium or other thermally conductive fluid, and the channels are sealed, such as by lamination of the piezoelectric actuator over the cavity.
In operation, the pump circulates fluid within the channels and preferably carries heat away from heat generating integrated devices, such as fast switching transistors in a logic circuit of a dynamic random access memory (DRAM) chip. In the illustrated embodiment, the channels communicate the heat outwardly from these buried devices, and a heat sink, such as a conventional copper plate, communicates heat away from the die. Moreover, a series of pumps can be arranged in sequence along the channels, and operated in sequence to serve collectively as a peristaltic pump.